The present invention relates to the recovery of cesium formate and/or rubidium formate from a mixed alkali metal formate blend that is in solution.
Cesium formate solutions, such as cesium formate brines, are a high-density, low-viscosity clear brines that are quite useful as drilling fluids, completion fluids, intervention fluids, and suspension fluids in the oil and gas field recovery operations in wells and reservoirs. Cesium formate is quite useful in HPHT (high pressure high temperature) drilling sites. While cesium formate has a density or specific gravity of 2.2 to 2.4 s.g., many times there is a need to formulate a specific gravity or density that is below the specific gravity for a pure cesium formate brine based on the particular demands and needs of the particular well site. When a lower specific gravity or density is required, many times potassium formate, which has a lower density, is used to reduce the overall density of the brine or fluid. By using various ratios of cesium formate to potassium formate, a wide range of specific gravities are achievable, such as 1.57 to 2.3 s.g. The potassium formate is fully miscible with the cesium formate, thus making it a useful blend for oil and gas recovery efforts. Thus, when cesium formate solution, such as cesium formate brine, is commercially supplied to end users, such as drilling rigs, each well will have a unique need with regard to the density of fluid to use and, therefore, individual specialized blends are created to achieve a very specific density of fluid by using, typically, cesium formate in combination with potassium formate, though other formates, such as sodium formate and lithium formate, may be used, though to a far lesser extent. When the particular use of the brine or fluid is completed, many times the brine or fluid is recovered to the extent possible due to its value, and then sent back to the supplier.
However, this individual need for specialized blends per drilling site results in a large inventory of different returned individual blends from each well site. For instance, one blend may be 1.6 s.g. and another blend used in another well site may be 1.7 s.g. and another blend used at a further well site might be 1.8 s.g. and so on. This results in hundreds and hundreds of liters of different blends. Since these blends are not discarded due to their valuable components of cesium formate and, to a lesser extent, potassium formate, their re-use in subsequent drilling sites would be very desirable. However, because cesium formate and potassium formate are totally miscible with each other and cannot be physically separated based on density or simple separation techniques, this creates a problem with regard to their subsequent use. Further, as indicated, the fact that each blend is individualized for a particular well site makes it quite difficult to provide this blend to a subsequent user unless their density demands (and amounts) are identical with the blend that is in inventory. Generally, when an individualized density brine is created, one starts from the highest density which is essentially a pure or nearly almost pure and nearly saturated cesium formate solution, which is 2.2 to 2.4 s.g. at 25° C., and then using potassium formate, the density is reduced to desired needs. Thus, the most efficient way to dial-in a density is to start with cesium formate and then to lower the density using potassium formate. Since many of the blends returned to the supplier/formulator after use are of varying amounts with regard to cesium formate and potassium formate, and because the cesium formate cannot be separated by basic physical separation techniques, this creates a large inventory of rather unuseful blends. Essentially, what is needed is to return the components to their near individual state or, in other words, substantially separate the blend into its individual formate components so that the starting cesium formate can again be used as the starting point and then adjust the density of the formate solution using potassium formate or other formates to desirable densities. Having a standard starting material, such as cesium formate or almost pure cesium formate solution or brine, with a standard known density range permits one to create a single usable inventory that can then be used and adjusted per individual well needs.
Accordingly, there is a need in the industry to provide cost-efficient, yield-efficient, and/or effective methods to separate a mixed alkali metal formate blend so as to recover and restore the cesium formate and potassium formate (and/or other formates) from the mixed alkali metal formate blend for subsequent use.